In 1955, Monaco joined the Universal Postal Union. In 1937, the Principality responded to growing interest from philatelists by creating a postage stamp office. The accession to the throne in 1949 of Prince Rainier III led to an increase in the importance of philatelic issues of the principality. During his reign, the Prince was personally involved in all aspects of the development of the designs and form of Monaco's philatelic issues. He is credited with saying that postage stamps are a country's "best ambassador." The prince was a famous philatelist; his collection formed the basis of the Museum of Postage Stamps and Coins of Monaco.